RCU Forums

I've had a lot of problems with SIG dope recently. Been covering with dope for about 50 years but was away from the hobby for several years (new house), then when returning bought some new SIG clear butyrate to cover with (using silk, nylon, silron, silray, Skyloft, etc. - doesn't seem to matter which fabric). Still have a lot of the older colored SIG dope and I believe that's ok - the problem seems to be just with the clear.

Procedure used to be, 2 coats of clear on the framework, sanded lightly, attach wet covering by brushing through the weave and rubbing it down with the fingers. After everything is covered, start the weave-filling coats of clear. In some cases, I've had problems with the covering "letting go", while putting on succesive coats of clear. Like it didn't stay stuck to the framework. Other times, everything seems to be fine but after painting on the main color, then while taping off and painting other colors (like stripes or whatever) when pulling the tape off it will lift the covering off sheeted areas under where it is taped off. Doesen't pull the covering all the way off the model, but if you watch closely you can see the covering separate from the wood directly below the tape, but the covering will immediately lay back down flat and "look" like it's stuck tight.

I have big problems getting the covering to stay stuck down when covering over concave ares. Even when covering wet, and the covering is conformed to the concave area, after brushing clear butyrate through the covering, as the covering dries out, it will lift up and not stick to the concave area below. It just "bridges accross". It's like the butyrate does not soften then stick to the coats applied to the balsa.

I contacted the "SIG Factory Fliers" (as their catalogs used to like to refer to them) and asked what the problem was. Here is the response I got (direct quote form the email I received):

"We have had the same problem with the clear Supercoat. The EPA have change the
base for the clear. Try using the Lite-Coat clear with very light coats in the
the place you are having problems with. On the top of the wing have a joint in
the center that way it will lay down.
SIG MFG."

I tried using the Lite-Coat clear as they suggested but, frankly, I can't tell ANY difference between Lite-Coat and regular SIG clear butyrate, both in the way it sticks and the amount of shrinkage.

Has anybody else had similiar experiences? Would I have better luck using Nitrate dope to apply the covering and then switch to butyrate?

I'm wondering if changes by the EPA (that we haven't heard about) may have affected the products we have been used to using over the years. I know I used to NEVER have problems with silk and dope, and now it seems like it's nearly impossible to "get it right".